Like silicone oils and silicone rubbers, silicone-based pressure-sensitive adhesives have heat resistance, freeze resistance, electric insulation, weather resistance, water resistance and non-toxicity characteristic of the polysiloxane structure involved. They are also highly adherent to fluoro-resins and silicone rubbers which are difficult to bond with organic polymer-based pressure-sensitive adhesives. Thus they comply with a wide variety of substrates and are used in a wide range of application. They are especially suited for use in the manufacture of electronic parts, because of high purity, high heat resistance, low Tg, low modulus of elasticity, high electric resistance and low dielectric constant.
Prior art silicone-based pressure-sensitive adhesives are used in the application where bond strength is not so required, for example, as protective tape, securing tape or masking tape and for substrate lamination. However, these adhesives are recently required to develop initially adhesive bond (or tackiness) and subsequently permanent adhesion to various substrates.
In one application, a silicone adhesive which changes from adhesive bond to permanent adhesion is expected, from the reliability standpoint of silicone resin, to find use as a dicing/die bonding tape which is believed useful in the manufacture of semiconductor devices.
In the manufacture of semiconductor devices, a large diameter silicon wafer is secured by a pressure-sensitive adhesive tape (known as dicing tape) and subjected to a dicing (sawing and separating) step where the wafer is divided into semiconductor chips. The chips are then peeled from the dicing tape. The chip thus taken out is secured to a lead frame with a curable liquid adhesive (or die bonding agent) through heat compression bonding. In the current industry, a simpler process is needed, and the contamination of semiconductor parts with fluid ingredients from the liquid adhesive is also an issue of concern. It is then desired to have a dicing/die bonding tape in the form of a pressure-sensitive adhesive sheet serving as both the pressure-sensitive adhesive layer of the dicing tape and the die bonding agent. The pressure-sensitive adhesive (dicing)/die bonding layer needs to develop a tack force (or attachment) to withstand the dicing operation and to adhere to the chip being taken away in the initial dicing step and needs to further develop a strong bond to the lead frame in the subsequent die bonding step.
The pressure-sensitive adhesive (dicing)/die bonding layer of the dicing/die bonding tape is proposed in JP-A 9-67558 as comprising polyimide resins. On account of a high glass transition temperature (Tg) and a high modulus of elasticity, the polyimide resins are insufficient to mitigate the thermal stress between bonded substrates of semiconductor parts. To enhance reliability, there is a need for a dicing/die bonding tape comprising a silicone resin having a low Tg and a low modulus of elasticity enough for stress mitigation.
Silicone pressure-sensitive adhesives of the type that changes from tackiness to permanent adhesiveness are disclosed in JP-A 7-53871, JP-A 7-53942 and U.S. Pat. No. 5,340,887 (JP-A 7-70541). They establish a bond through crosslinking and curing with moisture. However, a long term of several days to several weeks is necessary until these pressure-sensitive adhesives acquire a substantial bond strength. Such extremely low productivity prevents the adhesives from being applied as the dicing/die bonding layer for use in the manufacture of semiconductor devices.